Biodiversity and decomposition in experimental grassland ecosystems

We examined the impact of biodiversity on litter decomposition in an experiment that manipulated plant species richness. Using biomass originating from the experimental species richness gradient and from a species used as a common substrate, we measured rates of decomposition in litterbags in two locations: in situ in the experiment plots and in an adjacent, common garden. This allowed us to separate the effects of litter quality and decomposition location on decomposition. We found that plant species richness had a significant, but minor negative effect on the quality (nitrogen concentration) of the biomass. Neither litter type nor location had a consistent effect on the rate of carbon and nitrogen loss over a 1-year period. Thus, the increased productivity and corresponding lower soil available nitrogen levels observed in high diversity plots do not lead to faster litter decomposition or faster nitrogen turnover. This supports the hypothesis that increased productivity corresponding with higher species richness results in increased litter production, higher standing litter pools and a negative feedback on productivity, because of an increased standing nitrogen pool in the litter.